This invention relates to an image input device for use in combination with an identification system which carries out identification of a fingerprint.
An identification system of the type described identifies each person by the use of attributes of fingerprint impressions that are unique for each person and remain unchanged throughout one's life. It has been a recent trend that the identification system is used not only in a criminal investigation but also in a cash dispensing system or a person identifying system of checking entrance and exit to and from an offlimits zone.
In such a cash dispensing system or the like, identification should accurately be carried out in a real time manner. A distinct and clear fingerprint impression must therefore be derived from a fingertip which will be called an object. In addition, a false or forged fingerprint impression might willfully be used in the cash dispensing system. Therefore, such a false fingerprint impression should be distinguished from an impression derived from a true or natural fingerprint.
In U.S. Pat. No. 3,975,711 issued to D. H. MacMahon, an image input device is disclosed which comprises a transparent prism of an isosceles right triangle having a pair of equilateral sides and a hypotenuse. An input plane is defined along the hypotenuse so as to place a fingertip. A parallel light beam illuminates the fingertip on the input plane to provide an image. The image is sent to an optical pickup system to be converted into an image signal on one hand and is visually monitored through an optical system by an observer or operator on the other hand.
With this structure, it is possible to detect whether or not an impression of the fingerprint is adequate. However, the image input device should be supervised by the observer or operator. In other words, automatic supervision is impossible with the image input device.